Multiply -2 to x - y = 3.
We will have -2x + 2y = -6
Combine both equations to get -2x + 2y = -2x + 2y, which means y = y
Substitute this into the orginal equation to get -2x + 2y = -6
This means that there are infinitely many solutions.
You just need to choose a value of y, substitute it into the equation, get a value of x, and these pair of values will be a solution.